The soy isoflavone daidzein improves the capacity of tamoxifen to prevent mammary tumours

Andreas I. Constantinou*, Bethany E P White, Debra Tonetti, Yanan Yang, Wenzhong Liang, Wenkui Li, Richard B. Van Breemen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

65 Scopus citations


The aim of this study was to determine how the efficacy of tamoxifen is affected when combined with soy isoflavones. To address this, female Sprague-Dawley rats were placed on diets supplemented with tamoxifen, genistein, daidzein, or a combination of each isoflavone with tamoxifen; a week later mammary tumours were induced by 7,12 dimethylbenzanthracene. The most effective diet was the tamoxifen/daidzein combination. It reduced tumour multiplicity by 76%, tumour incidence by 35%, tumour burden by over 95%, and increased tumour latency by 62% compared with positive controls. The tamoxifen/daidzein combination diet was in all aspects more effective while the tamoxifen/genistein combination was less effective than the tamoxifen diet. The tamoxifen/daidzein diet significantly decreased 8-oxo-deoxyguanosine levels (an indicator of oxidative DNA damage) in the mammary glands. This study conclusively shows for the first time the combination of daidzein with tamoxifen produces increased protection against mammary carcinogenesis, while the combination of genistein with tamoxifen produces an opposing effect when compared with tamoxifen alone.

Original languageEnglish (US)
Pages (from-to)647-654
Number of pages8
JournalEuropean Journal of Cancer
Issue number4
StatePublished - Mar 2005


  • Breast cancer
  • Chemoprevention
  • DMBA
  • DNA damage
  • Daidzein
  • Equol
  • Genistein
  • Isoflavones
  • Soy
  • Tamoxifen

ASJC Scopus subject areas

  • Oncology
  • Cancer Research


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